1. Field of the Invention
Composite solid propellants commonly consist of one or more solid inorganic or organic oxidizer materials uniformly dispersed in a matrix of fuel binder material. In addition such propellants often contain solid and/or liquid additives to enhance the ballistic and/or physical performance of the finished product. Composite solid propellants are commonly made by mixing the solid ingredients with the liquid matrix ingredient, which are solidified after a uniform dispersion of the solid materials has been obtained.
Due to increased operational requirements, one of the problems to which a solution had to be found, was to provide a composite solid propellant having increased burning rates. One method of achieving such increased burning rates was the addition to the composite solid propellant of a highly efficient catalytic combustion modifier, which may also be referred to as a combustion or burning rate catalyst, and this invention, therefore, relates to certain ferrocene compounds that may be added to the composite solid propellant to increase the burning rate thereof.
2. Description of the Prior Art
Ferrocene (dicyclopentadinyl iron) has been used as a catalytic combustion modifier in composite solid propellants for many years, despite many disadvantages which limit its use. It is a solid having only limited solubility in the commonly used fuel binder matrix materials. Thus, only a limited amount of ferrocene will be dissolved in the matrix, larger amounts being dispersed as solid particles. The microscopically uniform distribution necessary for the maximum catalytic effect is, therefore, impossible to obtain. A more significant disadvantage of ferrocene, however, is its physical instability in composite propellants. Although the causitive mechanism is not fully known, but may be associated with the compound's inherently high vapor pressure, ferrocene is gradually lost from composite solid propellants with which it is used. The loss is greatest at the elevated temperatures commonly encountered during the processing of propellants, but occurs even during storage of the finished propellant charges. Thus, the ferrocene content of a composite solid propellant charge does not remain constant, as desired, but gradually decreases as ferrocene is lost. Also, part of the ferrocene loss from the mass of the propellant charge is deposited on the exposed surfaces of the charge, such as the central perforation of a star-perforated charge.
Many unsuccessful attempts have been made to overcome or circumvent the undesirable loss of ferrocene from composite solid propellants. Excess ferrocene has been added during processing since this is when much of the loss occurs, so that the desired level will be obtained, at least temporarily. This procedure will not prevent the loss of catalysts during storage. Complex solid polymeric forms of ferrocene have been substituted for the simple compound, but have been found to be insoluble in the binders and inferior in respect to catalytic ability.
Liquid ferrocene compounds have been used with some success in overcoming the difficulties associated with the use of ferrocene itself. These liquid compounds generally consist of a ferrocene radical having a side chain attached to the ferrocene radical, which produces a liquid product with a higher molecular weight which is beneficial in decreasing the vapor pressure of the burning rate modifier. Thus, some improvements in volatility are realized by the use of these liquid compounds. However, the gains in decreasing the volatility of the ferrocene unit are realized only at the expense of the catalytic activity of the combustion modifier. In most instances, these liquid ferrocene compounds have decreased percentages of iron which results in a loss in efficiency of catalytic activity. In addition, the low molecular weight liquid ferrocene compounds have problems associated with freezing point, in that on long term storage of propellants at low temperatures, the liquid ferrocene compounds tend to crystallize, which results in a change in the physical properties of propellant under these conditions. This undesirable situation restricts the low temperature storage limits at which propellant can be maintained. In addition, many of the liquid ferrocene compounds have a pronounced tendency to bleed out of the propellant and migrate into the inert components in a solid propellant rocket motor. This problem causes a decrease in the physical properties of the inert components and may result in motor failure.
In order, therefore, to overcome the problems that existed, where the use of ferrocene compounds were concerned, the instant invention deals with and explains the manner of producing a solid propellant wherein the ferrocene compounds are utilized as a combustion catalyst to increase the burning rate of the solid propellant.